1. Field of the Invention
The present invention relates to fused alumina particles coated with aluminum titanate, a process for producing the same, abrasive grits of the coated fused alumina particles, and a grinding wheel and coated abrasive using said abrasive grit.
2. Description of Related Art
As defined in JIS R6111-1987 for Artificial Abrasives, alumineous abrasives produced by fusing Baeyer alumina in an electric furnace include white alumineous abrasive (WA), pink alumineous abrasive (PA), monocrystalline alumineous abrasive (HA), and the like. The toughness of the abrasive is increased from WA to PA to HA (HA&gt;PA&gt;WA), but they still do not have suitable grinding qualities for tool steel or other hard materials. Thus, attempts have been made to coat the surface of the fused alumina with various additives to improve the grinding qualities thereof.
For example, JP-B-39-25620 discloses that a fused alumina abrasive grit is coated with 0.5 to 2.0% of an iron compound and heated to 700.degree. to 950.degree. C. to form a thin film of iron oxide on the abrasive grit. JP-B-40-16594 discloses that a fused alumina abrasive grit is coated with 0.01 to 1.0% of a chromium compound and heated at 800.degree. to 1,400.degree. C. to form a thin film of chromium oxide on the surface of the abrasive grit. JP-B-44-637 discloses that a fused alumina abrasive grit is coated with 0.2 to 2.0% of a copper compound and heated at 900.degree. to 1,250.degree. C. to form a thin film of copper oxide on the surface of the abrasive grit. JP-B-44-638 discloses that a fused alumina abrasive grit is coated with 0.2 to 2.0% of a nickel compound and heated at 800.degree. to 1,000.degree. C. to form a thin film of nickel oxide on the surface of the abrasive grit.
These coating layers are to remove micro defects of fused alumina particles which appear when the particles are crushed from ingot and do not essentially improve the grinding qualities of the abrasive grits.
Further, these coating layers physically cover the surface of the abrasive grit and can be easily peeled off. As a result, the grinding qualities of the abrasive grit are not improved.
JP-B-39-11196 discloses that a fused alumina is coated with colloidal alumina. JP-B-40-14357 discloses that a fused alumina is wetted with an organic adhesive solution, powders of refractory materials such as a Fe.sub.2 O.sub.3 --ZnO--MnO mixture, a TiO.sub.2 --SiO.sub.2 --ZnO mixture or TiO.sub.2 are applied on the wetted fused alumina, and the fused alumina with the refractory powders is heated to fuse the refractory powders onto the surface of the fused alumina.
These coating layers are to improve the wetting of the abrasive grit with a binder during production of a grinding wheel, so that the toughness of the grinding wheel is improved. Thus, the abrasive grit itself is not essentially improved and an improvement in the grinding qualities of the abrasive grit is not attained.